What is the best treatment approach for an adult patient with iron deficiency anemia?

Treatment of Iron Deficiency Anemia in Adults

Start with oral ferrous sulfate 325 mg (65 mg elemental iron) once daily, and only escalate to intravenous iron if the patient has active inflammation, malabsorption, intolerance to oral therapy, or fails to respond within 4 weeks. 1, 2

Initial Treatment Strategy

Oral iron is first-line therapy for most adults with iron deficiency anemia:

• Prescribe ferrous sulfate 325 mg once daily (equivalent to 65 mg elemental iron), or alternatively ferrous fumarate or ferrous gluconate 1, 3
• Do NOT defer iron replacement while awaiting diagnostic workup unless colonoscopy is imminent 1
• If gastrointestinal side effects occur, reduce to one tablet every other day rather than discontinuing—this maintains efficacy while improving tolerability 1, 2
• Higher doses (>100 mg elemental iron daily) provide no additional benefit and cause more side effects 2

Monitor response at 4 weeks:

• A hemoglobin rise ≥10 g/L within 2 weeks strongly confirms iron deficiency even if initial labs were equivocal 1, 2
• Continue treatment for approximately 3 months after hemoglobin normalizes to replenish bone marrow iron stores 1

When to Use Intravenous Iron

Switch to IV iron in these specific situations:

• Active inflammatory conditions (IBD, chronic kidney disease, heart failure) where hepcidin blocks oral iron absorption 1, 2
• Documented malabsorption (celiac disease, atrophic gastritis, post-bariatric surgery) 1, 4
• Intolerance to oral iron despite alternate-day dosing 1
• Inadequate response to 4 weeks of oral therapy 1, 2
• Ongoing significant blood loss (e.g., portal hypertensive gastropathy, angioectasias) 1
• Second or third trimester of pregnancy 4

Critical Diagnostic Considerations

Before initiating treatment, confirm iron deficiency:

• Serum ferritin <45 ng/mL in anemic patients is the single most useful marker 1, 2
• In inflammatory conditions, ferritin up to 100 ng/mL may still indicate iron deficiency—add transferrin saturation (<20%), soluble transferrin receptor, or reticulocyte hemoglobin to confirm 1, 2

Identify the underlying cause:

• In men and postmenopausal women, perform bidirectional endoscopy (gastroscopy and colonoscopy) to exclude gastrointestinal malignancy 1
• Screen for celiac disease serologically in all patients 1
• Evaluate for Helicobacter pylori infection 1
• In premenopausal women under 40 without alarm features, bidirectional endoscopy may not be required 5

Management of Refractory or Recurrent Cases

If anemia persists or recurs despite adequate iron replacement:

• Investigate the small bowel with capsule endoscopy (preferred) or CT/MR enterography for angioectasias, inflammatory disease, or neoplasms 1
• Treat identified angioectasias with argon plasma coagulation or endoscopic band ligation while continuing iron replacement 1
• Consider long-term iron replacement therapy when the cause is unknown or irreversible 1

Special Population Considerations

In inflammatory bowel disease:

• Determine whether anemia is from inadequate absorption or blood loss 1
• Treat active inflammation aggressively to enhance iron absorption 1
• Use IV iron preferentially when active inflammation compromises absorption 1

In elderly patients with comorbidities:

• Carefully weigh risks versus benefits of invasive endoscopic investigations 1
• Consider CT colonography as an alternative to colonoscopy in those unsuitable for invasive procedures 1, 2
• Recognize that anemia is often multifactorial in this population 1

In chronic heart failure or chronic kidney disease:

• IV iron may improve symptoms and quality of life even with functional iron deficiency 1
• Refer to specialist guidelines for these specific populations 1

Common Pitfalls to Avoid

• Do not assume dietary deficiency is the primary cause in adults—gastrointestinal bleeding and malabsorption are far more common, especially in men and postmenopausal women 2
• Do not use high-dose oral iron regimens—100 mg elemental iron daily is as effective as higher doses with fewer side effects 2
• Do not persist with oral iron in active inflammatory states—hepcidin-mediated blockade renders oral iron ineffective regardless of dose 2
• Do not skip investigation in men or postmenopausal women—they require endoscopic evaluation to exclude malignancy 1
• Do not forget to continue iron replacement post-transfusion—packed red cell transfusion does not replenish iron stores 1